HYPHOMYCETES.--The moulds are much more universal in their habitats, especially the _Mucedines_. The _Isariacei_ have a predilection for animal substances, though not exclusively. Some species occur on dead insects, others on decaying fungi, and the rest on sticks, stems, and rotten wood. The _Stilbacei_ have also similar habitats, except that the species of _Illosporium_ seem to be confined to parasitism on lichens. The black moulds, _Dematiei_, are widely diffused, appearing on herbaceous stems, twigs, bark, and wood in most cases, but also on old linen, paper, millboard, dung, rotting fruit, &c., whilst forms of _Cladosporium_ and _Macrosporium_ are met with on almost every kind of vegetable substance in which the process of decay has commenced. _Mucedines_, in some instances, have not been known to appear on more than one kind of matrix, but in the far greater number of cases they nourish on different substances. _Aspergillus glaucus_ and _Penicillium crustaceum_ are examples of these universal _Mucedines_. It would be far more difficult to mention substances on which these moulds are never developed than to indicate where they have been found. With the species of _Peronospora_ it is different, for these are truly parasitic on living plants, and, as far as already known, the species are confined to certain special plants, and cannot be made to vegetate on any other. The species which causes the potato murrain, although liable to attack the tomato, and other species of _Solanaceæ_, does not extend its ravages beyond that natural order, whilst _Peronospora parasitica_ confines itself to cruciferous plants. One species is restricted to the _Umbelliferæ_, another, or perhaps two, to the _Leguminosæ_, another to _Rubiaceæ_, two or three to _Ranunculaceæ_, and two or three to _Caryophyllaceæ_. All the experiments made by De Bary seem to prove that the species of _Peronospora_ will only flourish on certain favoured plants, to the exclusion of all others. The non-parasitic moulds are scarcely exclusive. In _Oidium_ some species are parasitic, but probably all the parasitic forms are states of _Erysiphe_, the non-parasitic alone being autonomous; of these one occurs on _Porrigo lupinosa_, others on putrefying oranges, pears, apples, plums, &c., and one on honeycomb. _Acrospeira_ grows in the interior of sweet chestnuts, and we have seen a species growing within the hard testa of the seeds of _Guilandina Bondue_, from India, to which there was no external opening visible, and which was broken with considerable difficulty. Several _Mucedines_ are developed on the dung of various animals, and seldom on anything else.